Stabilization of television amplifiers



1940- K. SCHLESINGER 2,186,933

STABILIZATION OF TELEVISION AMPLIFIERS Original Filed July 23, 1936 mpgm Patented Jan. 9, 1940 UNITED STATES STABILIZATION OF TELEVISION 1AMPLIFIERS Kurt Schlesinger, Berlin-Friedrichshagen, Germany, assignor,by

mesne assignments, to

Loewe Radio, Inc., a corporation of New York *Qriginal application July23,1936, Serial No. 92,151. Divided and this application "August 10,1937, Serial No. 158,390. In Germany July 3 Claims.

This application is a division of my application 92,151, filed July 23,1936, which issued asPatent 2,163,219, June 20, 1939.

Photo-cell amplifiers for television transmitters, which are furnishedwith resistance-condenser coupling or with galvanic coupling and whichare also referred to as low-frequency amplifiers, have as is well knownthe tendency to flutter when operated by mains-connected apl paratus orby central batteries. By this there is meant a slow pulsating action ata frequency in the vicinity of the lowest transmission frequency, whichis caused by reaction coupling by way of the internal resistance of theanode potential source. 7

The present invention is directed to low-frequency amplifiers which arealso enabled to amplify very low frequencies and in some cases toamplify direct current and shows a. method used fluttering effect.

This method will be clearly understood by way of example shown in theaccompanying drawing in which there is shown an amplifier circuit fortelevision purposes using a method for preventing fluttering of theanode potential in accordance with the invention.

In this drawing there is shown an exemplary embodiment of the methodaccording to the invention for neutralizing single tube stages againstfluttering effect which method is used for screening grid tubes. of thefact that the powerful current of one preceding amplifier stage,forexample, produces a 35 variation in the anode potential of this feedline 8 via the circuit elements of the feed line 8.

It will be assumed that the feed line 8 experiences a potentialfluctuation in the positive direction which, when amplified by the tube(not shown) which is coupled via condenser 25 to tube 24, may lead tofluttering of the amplifier. This disturbance would disappear if it werepossible to prevent the anode potential of the tube 24 from fluctuatingin conformity with the potential of the feed line 8.

This is attained by coupling the screening grid 26 of the tube 24 to theline 8 so that the screening grid 25 experiences the potentialfluctuations of line 8. If the potential of line 8 becomes more forthese amplifiers for preventing effectively the The fluttering occurs byreason equal to the increase of its potential due to its connection tothe line 8. This compensation depends on the control exerted on theanode current by the screening grid 26., and it is possible to regulateit by varying the degree of coupling of the screening grid 26 to theline 8 until the desired effect is obtained. The operating conditions ofthe tube 24 necessitate a definite bias for the screening grid 29 whichis permanently ad- ,iusted by a potential divider 28', 28". Since byreason of the working conditions of the tube 24 there is a limitation toa certain screening grid bias, it is impossible in many cases to adjustthe compensation point by means of ohmic resistance. According to theinvention, the adjustment of the compensation may take place by means ofa parallel condenser 29. This forms together with the condenser 39 acapacitative potential distribution which, therefore, does not afiectthe bias conditions of the screening grid 26. By the reduction of 39 andcorresponding increases of 29 it is possible in practice to perform acomplete stabilisation of the tube 24 in relation to slow fiuctuationsin the potential of line 8. Rapid fiuctuations or" line 8 are, in anycase eliminated in the ordinary way by the filter chain 3l/32.

It has been found in practice that a potential distribution of 6:4 mf.for 29:30 in an amplifier having stages and a preliminary tube providedgood results, when the screening grid coupling method was employed inthe two preliminary stages of the amplifier.

An additional means against fluttering resides in the use of asuccessive anode current filtering separated according to amplifiergroups. This filtering is effected by filter chains, which are to betraversed successively by the anode currents of the single amplifierstages. These filter chains consist of condensers with seriesresistances or series choke, the number traversed being dependcut on howfar the amplification stages in the whole amplifier arrangement aresituated towards the input end. This additional means is already used inthe circuit arrangement shown in Patent No. 2,163,219, issued June 20,1939.

I claim:

1. A television amplifier circuit arrangement which is also enabled toamplify very low frequencies comprising an amplifier tube having atleast four electrodes, a cathode, a control grid, a screening grid andan anode, an input and output circuit for amplifying the televisionimpulses, a common feed line circuit from a bias potential'source offluctuating potential for energizing the electrodes of the tube andcoupling means for supplying said screening grid with said potentialfluctuations, said coupling means consisting of a circuit connectionincluding a capacitive potential divider in combination with an ohmicpotential divider between the feed line and the cathode of said tube,said capacitive potential divider consisting of two condensers connectedin series and said ohmic potential divider consisting of two ohmicresistances connected in series and in parallel to said condenser-seriesconnection, the connection point of said condensers and said resistancesbeing connected to the screening grid of said tube, said condensershaving such values that the detrimental effect of the bias potentialfluctuations is compensated by supplemental variation of the anodecurrent of said tube due to the bias potential variations at thescreening grid.

2. A television amplifier circuit arrangement which is also enabled toamplify very low frequencies including a cascade connection of singleamplifier stages, each single stage comprising an amplifier tube havingat least four electrodes, a cathode, a control grid, a screening gridand an anode, an input and output circuit for ampliiying the televisionimpulses, a common feed line circuit from a bias potential source offluctuating potential for energizing the electrodes of the tube andcoupling means for supplying said screening grid with said potentialfluctuations, said coupling means consisting of a circuit connectionincluding a capacitive potential divider in combination with an ohmicpotential divider between the feed line and the cathode of said tube,said capacitive potential divider consisting of two condensers connectedin series and said ohmic potential divider consisting of two ohmicresistances connected in series and in parallel to said condenserseriesconnection, the connection point of said condensers and said resistancesbeing connected to the screening grid of said tube, said condensershaving such values that the detrimental effect of the bias potentialfluctuations is compensated by supplemental variation of the anodecurrent of said tube due to the bias potential variations at thescreening grid.

3. A television amplifier circuit arrangement which is also enabled toamplify very low frequencies including a cascade connection of singleamplifier stages with a series connection of filter chains in the anodefeed supply lines, each single stage comprising an amplifier tube havingat least four electrodes, a cathode, a control grid, a screening gridand an anode, an input and output circuit for amplifying the televisionimpulses, a common feed line circuit from a bias potential source offluctuating potential for energizing the electrodes of the tube andcoupling means for supplying said screening grid with said potentialfluctuations, said coupling means consisting of a circuit connectionincluding a capacitive potential divider in combination with an ohmicpotential divider between the feed line and the cathode of said tube,said capacitive potential divider consisting of two condensers connectedin series and said ohmic potential divider consisting of two ohmicresistances connected in series and in parallel to said condenser-seriesconnection, the connection point of said condensers and said resistancesbeing connected to the screening grid of said tube, said condensershaving such values that the detrimental efieot of the bias potentialfluctuations is compensated by supplemental variations of the anodecurrent of said tube due to the bias potential variations at thescreening grid, said filter chains consisting of a series connection ofseries resistances and earthing condensers, which are so arranged thatthe feed current of the stages which are situated towards the input ofthe whole amplifier arrangement have to transverse the filter elementsof the succeeding stages.

KURT SCI-ILESINGER.

